Dip coating is a well known method for depositing layered material onto a substrate. In many situations, it is desirable for the dip coated layer to have a substantially uniform thickness along the length of the substrate. During dip coating, however, sloping of the deposited layer may occur due to the acceleration of the substrate from 0 speed to the desired take-up speed and due to non-uniform gravitational flow from the starting point to where steady state is achieved, thereby resulting in a portion of the deposited layer exhibiting a non-uniform thickness. There is a need, which the present invention addresses, for new methods and apparatus that can minimize or eliminate the sloping phenomenon for layered material dip coated onto a substrate.
Conventional dip coating methods and apparatus are illustrated in Petropoulos et al., U.S. Pat. No. 5,578,410; Crump et al., U.S. Pat. No. 5,385,759; and Mistrater et al., U.S. Pat. No. 5,829,760.
The present invention is accomplished in embodiments by providing a coating method for a hollow substrate comprising:
(a) forming a seamed extended substrate unit comprised of a substrate extension device and the substrate, and employing a chuck assembly to internally grip the substrate;
(b) dip coating the extended substrate unit while the chuck assembly internally grips the substrate to deposit a layer first on the substrate extension device and then on the substrate; and
(c) separating, subsequent to the dip coating the extended substrate unit, the substrate extension device from the substrate.
In other embodiments, there is provided an apparatus comprising:
(a) a chuck assembly capable of internally gripping a hollow substrate; and
(b) a substrate extension device, coupled to the chuck assembly, positioned adjacent an end of the substrate resulting in a seamed extended substrate unit.
There is also provided in embodiments an apparatus comprising:
(a) a chuck assembly capable of internally gripping a hollow substrate; and
(b) a substrate extension device, not coupled to the chuck assembly, positioned adjacent an end of the substrate resulting in a seamed extended substrate unit.